The mouse hepatoma line, Hepa-1, has high activity of the cytochrome P-450 associated enzyme, aryl hydrocarbon hydroxylase (AHH), which is involved in the activation of polycyclic aromatic hydrocarbon (PAH) carcinogens. We isolated rare benzo(a)pyrene-resistant (BPr) mutants, and showed that they were deficient in AHH. Cell-cell hybridization experiments carried out so far show that most mutants are recessive and belong to a minimum of three complementation groups. We shall perform additional hybridization experiments to determine exactly how many complementation groups exist among our 200 mutants. Using SDS-PAGE electrophoresis and CO-difference spectrometry we shall investigate whether individual mutants are defective in the structure, or in the amount of cytochrome P-450. We shall also assay NADPH-cytochrome c reductase, epoxide hydrase, UDP-glycuronosyl transferase and glutathione S-transferase to see if any mutants are altered in these enzymes, and continue to investigate whether any are defective in the cytosolic receptor protein for PAH's. We shall also attempt to design selection procedures for isolating epoxide hydrase and UDP-glucuronosyl transferase-deficient mutants, and revertants of the BPr mutants. We are also attempting to design a procedure for isolating bona fide AHH-deficient mutants of the rat hepatoma line, HRIIE.